Although many human resources departments conduct exit interviews, I would argue that they are not worthwhile. My main reason for saying this is that there is no reason to believe that they will yield authentic results.
An exit interview is typically conducted when an employee is leaving a firm. That employee may have been laid off, may have been fired for cause, or may have resigned to pursue another job opportunity. HR departments typically ask them questions concerning how they felt about the firm. Supposedly, these questions are meant to help the firm improve itself.
The problem is that exiting employees have little incentive to be truthful. In fact, they likely have reason to lie or to be less than forthcoming. Employees are unlikely to say anything very negative about a company because they might think that they should not burn any bridges. If they say things that are negative, they fear, their former bosses might be offended and might find ways to harm their careers. For example, a boss might tell counterparts in other firms that the employee has various flaws, thus making that employee less likely to get good jobs.
Exit interviews could be valuable, but only if they were guaranteed to get valid data. Since they are not guaranteed to yield such data, these interviews are not worthwhile.